摘要:

The design and operational characteristics of a capacitance bridge detector and accompanying signal lock system are presented. The signal lock is especially well suited for the measurement of small changes in ion concentration during photochemical experiments, thereby alleviating problems caused by resonant frequency shifts.

ISSN:0034-6748    

DOI:10.1063/1.1139433

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We have developed a technique to measure the frequency‐dependent specific heat of a liquid over a frequency range exceeding five decades, 0.01–3000 Hz. The measurement is not performed adiabatically, but rather relies on heat diffusion from a thin, planar heater immersed in the liquid sample. The spectrometer has been used to study organic liquids near the glass transition.

ISSN:0034-6748    

DOI:10.1063/1.1139434

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We studied the sensitivity of a radiation detector based on metastable superconducting grains. Radiation is detected by the phase transition from the superconducting to the normal‐conducting state of a grain induced by energy absorption. Metastable states of tin and cadmium grains were tested. The phase boundary of a large sample of grains was found to be broadened due to variations of the phase diagrams of single grains. Therefore, the use of superconductors with a low critical temperatureTcand an operation temperature close toTcseems advisable to increase the sensitivity of the detector. For Cd grains a sensitivity normalized to the grain volume of 12 eV/&mgr;m3was achieved for the detection of &ggr; rays. These grains showed an instability in the superconducting to normal‐conducting phase transition for temperatures below 350 mK.

ISSN:0034-6748    

DOI:10.1063/1.1139383

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The detailed description, the experimental demonstration, and the design of single‐mode microwave cavity applicators are presented. These microwave applicators utilize an internally tuned, single‐mode (or selective multimode) cylindrical cavity to focus and match microwave energy into cylindrical rod, disk‐, or slab‐shaped material loads. The combination of mode focus control and variable, internal cavity matching allows the efficient coupling of microwave energy into a wide range of solid material loads. The experimental operation of these applicators is demonstrated for low loss to lossy materials, which include nylon, water, and semiconducting silicon wafers. Overall microwave coupling efficiencies of 70%–95% were measured and experiments demonstrated the ability to precisely control material heating. The single‐mode fields can be used to heat and diagnose during processing, and on‐line process diagnosis was experimentally demonstrated using cavity perturbation theory. When using these cavity applicators, many system variables such as tuning control, cavity electric field strength, input, and reflected power are available as potential process system feedback signals for automated intelligent processing. These applicators can be used to carefully study the fundamentals of electromagnetic interactions of many materials. Applications include the electromagnetic heating of foods, semiconducting and biological materials, and the heating and curing of epoxy and composite materials.

ISSN:0034-6748    

DOI:10.1063/1.1139384

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A concept for a miniature, solid‐state gas compressor is examined. The device operates by the phased activation of voltage‐driven, electrostrictive ceramic blocks along a compression channel wherein a confined elastomer provides a motion‐amplifying medium for peristaltically closing the compression channel. The device is also self‐valving. Model estimates based on the nonlinear electromechanical parameters for paraelectric BaTiO3suggest that a small (∼5×5×9‐cm3), lightweight (∼1‐kg) device would supply ∼0.3 cm3per cycle at a compression ratio of 25:1 employing modest electric fields (∼20 kV/cm). At 500 Hz this corresponds to 38 mW of ideal Joule–Thompson refrigeration at 4.2 K using He gas. The efficiency of the device is estimated to be ∼85% (not including the power supply). A three‐cell mechanical simulator of the concept was built and tested, and it was demonstrated that compression and self‐valving can be achieved by peristaltically extruding an elastomer against a gas channel. An electronic power supply to drive the electrostrictive ceramics was designed, and a three‐cell supply was built and tested which demonstrated that voltages up to 150 V could be switched at frequencies up to 10 kHz using small, inexpensive components. A critique of practical considerations is given, and it is concluded that the concept is feasible but additional research is required in elastomeric materials and in fabricating relatively large ceramic capacitors (∼2×2×1 cm3). Currently available electrostrictive actuators are inadequate.

ISSN:0034-6748    

DOI:10.1063/1.1139385

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A novel precision capillary viscometer which has a time resolution of ±0.001 s is reported. The viscometer has been utilized to demonstrate that estimates of intrinsic viscosity (to within 3% of the infinite dilution value for polystyrene in benzene) can now be made, over a wide range of polymer molecular weights, for solutions from a single polymer concentration.

ISSN:0034-6748    

DOI:10.1063/1.1139386

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A new float flowmeter design is presented based on the null method, with electric output signal and either manual or automatic current control in a coil to bring the float back to zero position. The instrument concerned is a constriction‐type device and based on its theory a simple expression can be derived for describing the input–output relationship in quadratic terms. In addition to a description of the device, the static calibration curves using air at 295.16±0.50 K are also provided for volumetric flowrates ranging from 11 to 16 dm3/min and Reynolds numbers between 500 and 800. Typical inaccuracy is 1.8% of flowrate over this range.

ISSN:0034-6748    

DOI:10.1063/1.1139387

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The design and performance of a simple and efficient planar magnetron sputtering source using demountable targets are described. The design of the source enables sputtering of magnetic and nonmagnetic materials with equal ease.

ISSN:0034-6748    

DOI:10.1063/1.1139388

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A new scaling linkage is presented which allows arbitrary magnification or reduction of curves and drawings in theydirection while leaving dimensions in thexdirection unchanged. The anisotropic pantograph represents a significant simplification over previously reported devices capable of this operation. MagnificationsMyin the range 1.05–80.0 and reductionsRyin the range 0.0125–0.95 are obtained using a single operation, and the tracking accuracy is <±150 &mgr;m. With the aid of a circle template or flat compass, the device may be used to draw arbitrary ellipses. A method for effecting arbitrary shears, and various methods for arbitrary scaling in two orthogonal directions are outlined.

ISSN:0034-6748    

DOI:10.1063/1.1139389

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A simple method of measuring the spatial transfer function of a gradiometer, consisting of a flux transformer coupled to a SQUID, is presented and it is compared with theoretical predictions. Based, on this approach, a new method of reporting a gradiometer’s performance is proposed; the rejection factor is expressed in decibels obtained directly from the transfer function plot.

ISSN:0034-6748    

DOI:10.1063/1.1139390

出版商:AIP    

年代:1987

数据来源: AIP